Enhancement of conversion and selectivity by temperature-swing unsteady-state reaction method in shape-selective methylation of methylnaphthalene with ZSM-5

In order to enhance the conversion of shape-selective methylation of 2-methylnaphthalene with HZSM-5 for producing 2,6-dimethylnaphthalene, an important precursor of high performance polyester, effect of reaction method was investigated. It was found that an unsteady-state reaction method with adsorption at a low temperature and subsequent flush at somewhat elevated temperature was very effective for enhancing the conversion drastically. This new reaction method, named low temperature adsorption and flush (LTAF) method, made it possible to increase the conversion up to more than 70% without losing shape-selectivity, whereas, by the conventional steady-state reaction method, the conversion remained at 10-20% level due to restricted diffusion of naphthalene-ring compounds in the HZSM-5 pore which was essential for the shape-selectivity. By LTAF method, the methylation can be performed in the range of temperature lower than that required for steady-state reaction, and the methanol conversion as a side reaction was effectively suppressed.